This invention is related to seals for preventing fluid leakage and, more particularly, to seals used in power generators.
Within the power generation industry, large-scale power generators convert mechanical energy, typically the energy output of a turbine, into electrical energy. The basic components of such power generators are a frame-supported stator core that provides a high permeability path for magnetism and a rotor assembly positioned to rotate continuously within the stator core so as to induce electrical current through rotor-borne conductors moving through magnetic fields set up within the stator. The resulting current is carried by high-current conductors through and out from a housing surrounding the power generator, to flex connectors that provide the current to a plant bus for power distribution to consumers, commercial establishments, and other users of electrical power.
According to the well-understood physics of electrical conduction through a conductor, current arises as a result of the flow of xe2x80x9cfreexe2x80x9d electrons that move under the influence of an electric field through the conductor. In free space the electrons accelerate and continually increase their velocity (and energy), but within the crystalline material of a conductor the electrons are impeded by their continual collisions with thermally excited atoms arranged in a crystalline lattice structure in the conductor until a constant average xe2x80x9cdriftxe2x80x9d velocity is attained. As a result of these collisions, heat is generated raising the temperature of the conductor and the surrounding environment. This effect can be especially pronounced within large scale power systems where large currents are generated and carried by the high-current conductors described above.
To deal with these temperature effects, various cooling systems are employed within large-scale power generators. For example, channels within the frame housing, the stator core and rotor assembly channel can be added to the power generator system to provide an avenue for a cooling fluid to flow into and out of the housing to cool the components therein. Frequently, hydrogen gas (H2) is used as a cooling fluid. These cooling devices, however, pose collateral challenges. In order to be effective in cooling the components of the power generator, the cooling fluid (i.e., hydrogen gas or other fluid) must be appropriately channeled or otherwise directed to the components. When flowing in such a channel, the cooling fluid must be maintained therein lest it escape into the air surrounding the frame thereby losing its cooling effect while inadvertently contaminating the surrounding environment.
In order to circulate the cooling fluid throughout the power generator, large blowers are usually employed to provide pressure differentials that disperse the cooling fluid within the frame housing the stator core and rotor assembly. The pressure so created can be quite high. Thus, to maintain the cooling fluid within the appropriate channel within the frame housing the stator core and rotor assembly, the channel must be sealed. The seal relied on to seal a channel must be able to withstand considerable pressure. In the typical power generation context, a sealing device intended to maintain the cooling fluid within the fluid channel must effectively accommodate pressures of as much as 75 pounds per square inch gauge (PSIG).
Of particular importance are the seals employed where the high-current conductors extend through the housing. For cooling purposes, the high-current conductor usually has a hollow channel or bore extending axially within the conductor and through which a cooling fluid such as hydrogen gas (H2) is pumped. The cooling fluid flows under pressure through the bore and exits the bore through vent holes formed through the conductor, flowing into a fluid channel extending along the conductor. Alternatively, a second bore can be disposed inside the channel or bore of the high-current conductor. Cooling fluid is then pumped into the inner bore where it flows out through vent holes and circulates within the channel formed by the high-current conductor.
Various sealing mechanisms have been used with varying degrees of success in attempting to effectively and efficiently seal cooling fluid within designated fluid channels in a power generator. U.S. Pat. No. 2,950,403 by Kilner et al., titled Electrical Turbo Generators, for example, describes the use of gas-tight shroud rings to contain gas surrounding the connection between a collector lead and collector ring. U.S. Pat. No. 4,682,064 by Crounse et al. titled Coolant Gas Flow Separator Baffle For A Dynamoelectric Machine describes a flexible flange that is urged into tighter abutment with the stator as surrounding gas pressure increases. U.S. Pat. No. 5,866,960 by Meier et al., titled Gas-Cooled Electrical Machine describes sealing cooling channels using a sealing cap and screw connection through which a tube extends. Finally, in the context of a non-cooling use, U.S. Pat. No. 6,121,708 by Muller titled Slot Sealing Arrangement describes sealing the winding slot in a stator core from an air gap using convex-surfaced wedges.
In other contexts, though, use of a sliding seal has been proposed. For example, U.S. Pat. No. 4,076,262 by Deventer titled Sliding Seal describes generally a seal comprising a rigid base (e.g., a metal or hard resin) that connects to an object and a flexible protrusion from the base that pliably bends with a foreign object as the foreign object contacts the outer portion of the protrusion in a moving fashion (See U.S. Pat. No. 4,076,262 FIGS. 2 and 6). Thus, as illustrated therein, the seal does not so much slide relative to the foreign object as much as it bends therewith. U.S. Pat. No. 4,714,257 by Heinrich et al. titled Annular Sliding Body For A Sliding Seal And Process For Use Thereof describes a dual-piece device having a sliding ring and counter ring, wherein the former remains stationary while the later rotates annularly by sliding against the former.
These and other conventional seals, both in the context of power generation and in other situations, generally do not permit the seal to slide or otherwise move in response to thermal expansion, fluid pressure, or vibratory movements that occur during operation of the power generator. Conventional seal designs, at best, allow for thermal expansion on the high-pressure side of the seal during thermal cycling of the power generator. This is the case with the wedge-ring seal conventionally employed for sealing cooling fluid in a fluid channel surrounding a high-current conductor in a power generator. FIGS. 1 and 2 illustrate a conventional wedge-ring seal 20 used to seal hydrogen gas or other cooling fluid within a fluid channel 22 surrounding a high-current conductor 24 of a power generator.
The conventional wedge-ring seal 20 poses several distinct problems. Among these is the inability of the wedge-ring seal 20 to smoothly slide relative to a sleeve 26 or other fluid channel forming member, thereby resulting in abrading degradation of a surface 21 of the wedge-ring seal 20 when the wedge-ring seal 20 movingly contact a surface 27 of the fluid channel forming member. The wedge-ring seal 20 is typically formed of a conductive material such as copper and is brazed to the high-current conductor 24. The wedge-ring seal 20 is usually xe2x80x9cwedgedxe2x80x9d against the channel-forming sleeve 26, which is normally formed of fiberglass. The fiberglass sleeve 26 typically exhibits an abrading property, usually resulting from the machining of the fiberglass to form the dimensions of the sleeve 26 to accommodate the wedge-ring seal 20. Machining removes any resin layer that would otherwise provide smooth contact between the fiberglass surface 27 of the sleeve 26 and the surface 21 of the wedge-ring seal 20.
Instead of a smooth, resined layer on the surface 27 of the fiberglass sleeve 26, the surface 27 has minute shards of glass particles extending therefrom, thereby creating an abrasive layer. Thermal expansion, vibratory motion, and/or fluid pressure can force the wedge-ring seal 20 to move relative to the sleeve 26 against which the wedge-ring seal is wedged. When the wedge-ring seal 20 moves relative to the sleeve 26, the minute shards of glass embedded in the fiberglass surface 27 abrade the surface 21 of the wedge-ring seal 20 thereby causing the wedge-ring seal 20 to degrade.
Another distinct problem posed by the wedge-ring seal 20 is that the wedge-ring seal 20 must be fixedly connected to the high-current conductor 24 substantially spaced apart from the end portion of the high-current conductor 24. FIG. 1 illustrates the nature of the problem. As shown, the end portion of conductor 24 must be adapted to mechanically connect to a flange 28 (the xe2x80x9cair-side flangexe2x80x9d) so as to electrically connect the conductor 24 to a bus assembly for transferring current from the generator. An adaptive portion 30 provides mechanical support to secure the conductor 24 and the flange 28. The wedge-ring seal 20, of necessity, then, is spaced apart from the end-positioned connection. With the wedge-ring seal spaced apart from the end portion of the conductor 24, a significant portion of the surface area of the conductor 24 is precluded from receiving vent holes.
The absence of vent holes along the surface area occupied by the wedge-ring seal prevents cooling fluid from reaching the entire extend of the conductor 24. Although, alternatively, cooling fluid can be supplied at the end of the high-current conductor by supplying the fluid through a fluid channel contained within the bore of the high-current conductor itself, as described above, the fluid remains within the high-current conductor bore thereby preventing the fluid""s reaching the outer surface of the high-current conductor. Therefore, given the obstacles posed by the conventional wedge-ring seal 20, cooling is constrained to reach only part of the inner and outer surfaces of the high-current conductor, or extend over the entire length of the high-current conductor but reach only the inner surface thereof.
An additional, heretofore substantially unrecognized problem with a conventional wedge-ring seal 20 concerns the O-ring 28 that as perhaps best shown in FIG. 2 is positioned within in an O-ring gland 29 formed in the surface 21 of the wedge-ring seal 20 to prevent leakage of hydrogen gas or other cooling fluid from the fluid channel 22. Because the wedge-ring seal 20 is formed of a conductive material and is normally not insulated, electrical current flows along the entire surface of the wedge-ring seal 20 thereby flowing along the surface of the O-ring gland 29 as well. The current causes electrical loses and O-ring degradation due to corresponding temperature increases.
In view of the foregoing, the present invention advantageously provides an apparatus for sealing fluids under fluid pressure within a fluid channel. The apparatus specifically includes a seal that is connected to a conductor while being able to move, slidably and otherwise, relative to a surface portion of a fluid channel forming member positioned adjacent the conductor. Thus, the seal, according to the present invention, advantageously permits the seal to smoothly slide or otherwise move relative to a fluid channel in a power generator in response to thermal expansion during thermal cycling, changes in fluid pressure in the fluid channel, and vibratory motions that inevitably occur during operation of a power generator and cause the seal to move against the surface of the fluid channel.
The seal, moreover, is protected in several distinct ways. Firstly, the seal is insulated so as to inhibit electrical loses through the seal. The seal also is insulated so as to prevent the through-flow of current in and around portions of the conductor that are easily degraded by high temperatures and other current-related effects. Additionally, to protect the seal when the seal slidably or otherwise contacts the surface of the fluid channel, the surface of the seal is formed so as to be substantially immune from seal-degrading abrasions Thus, the seal substantially reduces or eliminates current flow that would otherwise cause electrical losses and generate temperature increases that can degrade the seal while being substantially immune from abrasions as the seal slidably or otherwise moves in contact with the fluid channel.
The apparatus thus provides particular advantages in the context of the power generation industry where the apparatus can be used effectively and efficiently to prevent leakage of fluid (e.g., hydrogen gas) in a large-sized, fluid-cooled power generator. The apparatus, among its various uses, specifically prevents leakage of hydrogen (H2) gas in a hydrogen-cooled power generator, the power generator including a stator having a stator core which provides a high-permeability path for magnetism and a high-current conductor extending from the stator to connect to a main lead positioned apart from the stator. The apparatus also preferably includes a sleeve positioned substantially around the high-current conductor and spaced apart therefrom so as to form a fluid channel bounded on a side by a portion of an outer surface of the high-current conductor and on another side by a portion of the inner surface of the sleeve to thereby define a fluid channel.
In order to seal the hydrogen gas within the fluid channel, a protected seal is positioned within the fluid channel between the high-current conductor and the sleeve to form an end boundary of the fluid channel. The seal preferably includes a seal body having a first surface portion that fixedly contacts an outer surface portion of the high-current conductor and a second surface portion that slidably contacts an inner surface portion of the sleeve so as to prevent leakage of hydrogen (H2) gas contained within the fluid channel. The seal is positioned to permit the second surface portion of the seal body to slidably move relative to the sleeve or otherwise movingly contact the sleeve in response to thermal expansion, fluid pressure, and vibratory motion.
Within the fluid channel, the seal divides the space immediately adjacent the high-current conductor into a first distinct region and a second distinct region. The seal, so positioned, then is able to prevent fluid flow between the distinct first and second regions while permitting sliding and other moving contact of the seal with an inner surface portion of the sleeve. In one embodiment, the seal specifically includes a seal body having an annular shape and being positioned to substantially surround portions of the high-current conductor while a surface portion of the seal slidably moves relative to the sleeve. A substantially centered opening extends through the annularly shaped seal body and is threaded so as to thread onto a correspondingly threaded portion of the high-current conductor.
Moreover, at least one sealing gasket gland, for example, can be formed in the outer surface of the annularly shaped seal body or, alternatively, is machined into the sleeve in order to position therein a sealing gasket that expands and contracts to maintain a secure seal against a surface portion of a fluid channel to thereby prevent fluid leakage from the channel. Preferably, the sealing gasket is provided by at least one O-ring positioned within at least one O-ring gland that extends along the circumference of the outer surface of the annular seal body. The O-ring abuttingly contacts and moves relative to the inner surface portion of the sleeve to thereby substantially prevent fluid flow from the first distinct region to the second distinct region adjacent to the high-current conductor.
The sliding seal further includes an abrasion abatement layer disposed on a surface portion of the seal body to prevent degradation of the seal as the seal slidably or otherwise moves relative to and comes in contact with a surface portion of the fluid channel. Preferably, the abrasion abatement layer is formed of a metallic material such as silver plating formed on a copper seal body. The abrasion abatement layer provides a xe2x80x9csoftxe2x80x9d metallic layer that interacts with the surface of the fluid channel to dispose within the interstices of any abrading particles extending from the fluid channel, thereby smoothing the fluid channel surface rather than being abraded by the surface. The seal body itself is advantageously formed from a material having the same thermal expansion coefficient as the conductor to which it connects.
The present invention also provides alternative means for insulating the seal body and sealing gasket from current through-flows into the seal body so as to minimize electrical losses and reduce or eliminate current-induced temperature increases in the seal body that would otherwise reduce the operational life and reliability of the sealing gasket. According to one embodiment, the apparatus preferably includes at least one sealing gasket gland positioned within the surface of the fluid channel. The seal is adapted so that at least one sealing gasket can be positioned in the at least one gland. Alternatively, the apparatus includes a separate insulating gasket for inhibiting current flow that would otherwise cause electrical loss and seal-degrading temperature increases in the seal.
Preferably, the seal includes an annular portion defining a seal body that is threaded so as to thread securely onto a correspondingly threaded end portion of a conductor positioned within or adjacent a fluid channel. Particular advantages of the present invention, however, also pertain to various embodiments of a sliding seal formed into shapes other than the hollowed-center annular shape. More generally, the apparatus includes a sliding seal formed to fit within a fluid channel having virtually any dimensions. The seal has both a first surface that fixedly contacts the high-current conductor, and a second surface that slidably contacts a surface portion of a sleeve or other fluid channel forming member that is spaced apart from the high-current conductor and that forms the fluid channel positioned adjacent the high-current conductor.
The second surface of the seal body slidably or otherwise moves relative to and movingly contacts with the fluid channel forming member in response to thermal expansion, vibratory motions, and changes in fluid pressure. The sliding seal, preferably also includes along the second surface a pliable and compressible surface portion that responds to the slidable movement of the seal by expanding or contracting, respectively, so as to prevent gaps between the second surface of the seal body and the surface of the channel forming member as the second surface slidably moves relative thereto. So too, in this general context, the present invention as already noted provides a seal substantially protected from current flow that would degrade the seal, especially the pliable and compressible surface portion, and from seal degrading abrasions as the seal movingly contacts the surface of the fluid channel forming member.
The present invention also provides a method for preventing leakage of a cooling fluid, such as hydrogen (H2) gas, in a fluid-cooled power generator. The method includes maintaining fluid in a fluid channel using a seal having a first surface fixedly connected to the high-current conductor. The method further includes slidably contacting a second surface of the seal to a surface portion of the fluid channel to thereby permit the seal to slidably move relative to the surface portion of the fluid channel, the surface having an abrasion abatement layer to prevent degradation of the seal.
The method so described further includes positioning a layer of sealing material on a high-current conductor, the conductor having a threaded outer surface, and threading the seal over the sealing material positioned on the threaded portion of the high-current conductor to thereby fixedly connect the seal and the threaded portion of the high current conductor to the sealing material positioned therebetween. Also the method can additionally include preventing conduction of current from the high-current conductor through the seal to thereby reduce current-induced degradations to the seal.